The present invention relates to an expansion mechanism for radial expansion of a medical device. More particularly, the invention relates to a compliant framework which conforms to the interior anatomy of a patients, e.g., interior blood vessel wall, with minimum gap. The framework provides structure for medical devices such as filter meshes, damming or occlusion methods, flow direction devices, and locating and measuring applications.
During open heart surgeries, such as coronary artery bypass graft, valve repair surgeries, thoracic aneurysm repair, removal of atrial myxoma, and septal defect repairs, currently the most common method of temporarily occluding the ascending aorta utilizes a mechanical cross clamp. Aortic occlusion is needed to establish isolation of coronary circulation from the peripheral circulatory system during cardiac arrest, so that peripheral organs would not be paralyzed by cardioplegic solution. An arterial cannula is commonly inserted in a patient""s aorta or femoral artery to provide return of oxygenated blood from a bypass-oxygenator machine, whereas a venous catheter is inserted into the right atrium, superior vena cava, or inferior vena cava to carry deoxygenated blood from the heart to a bypass-oxygenator machine. Other less common means of occluding the aorta include percutaneous balloon catheter occlusion, direct aortic balloon catheter (Foley) occlusion, aortic balloon occluder cannula, and an inflating diaphragm occluder (Hillxe2x80x94occlusion trocar).
Manipulation of ascending aorta during mechanical cross-clamping or other means of aortic occlusion often dislodges atheromatous plagues from the ascending aorta downstream to peripheral organs. Tissue debris, air, or calcium plaques may also arise from cardiac manipulation. Embolization of atheromatous plaques, tissue debris, or calcium plaques may lead to stroke, organ death or ischemia.
Devices for filtering blood have been designed to reduce a patient""s peri-operative risk of peripheral embolization, thereby reducing surgical morbidity and mortality. The vast majority of these devices are designed for permanent placement in veins, in order to trap emboli destined for the lungs, e.g., Kimmell, Jr., U.S. Pat. No. 3,952,747, Cottenceau et al., U.S. Pat. No. 5,375,612, Gunther et al., U.S. Pat. No. 5,329,942, and Lefebvre, French Patent No. 2,567,405, incorporated herein by reference. Few intravascular devices are designed for arterial use, e.g., Ginsburg, U.S. Pat. No. 4,873,978, Ing. Walter Hengst GmbH and Co, German Patent DE 34 17 738, da Silva, Brazil Patent Application No. PI9301980A, and Barbut et al, U.S. Pat. No. 5,769,816, all incorporated herein by reference, have been developed to entrap arterial emboli during open-heart procedures.
The aforementioned devices all have drawbacks in that a filter or membrane to entrap emboli is deployed by means of an umbrella mechanism, thereby failing to accurately follow the rough non-uniform contour of the internal blood vessel wall. A built-in spring offers the force to bring the frame into contact with the vessel wall. The umbrella frame, however, would segment the contact, thereby only assuring a seal at each discrete arm in contact. Moreover, in using the current filter devices, an operator has little or no feel for contact between the filter mechanism and the vessel wall. Further, current designs do not permit closure which is sufficiently tight and secure to prevent release of entrapped emboli.
A need exists for devices and methods which provide contact of medical devices and vessel walls with minimum gap, give an operator a feel for the vessel wall during deployment, and permit efficient and secure closure to ensure retention of entrapped debris.
The present invention relates to an expansion mechanism for radial expansion of a medical device. More particularly, the invention provides a compliant framework which conforms to a patient""s interior anatomy (such as a vessel wall) with minimum gap, provides structure for filter meshes, damming or occlusion devices, flow direction devices, locating and measuring applications, and provides a feel for the contour of vessel wall during deployment. The framework may be a metal, plastic, gel or foam.
In one embodiment, the device includes an elongate instrument which may comprise a cannula. A plurality of struts are arranged circumferentially around the elongate instrument. Each strut has two ends. The first end is pivotally connected to the elongate instrument while the second end expands radially outward. Each strut carries a wire or line having a proximal end and a distal end. The distal end of the line passes beyond the second end of the strut which carries it. The distal end of each line is attached to the strut immediately adjacent to the strut which carries it. In one embodiment, the framework has two struts and two lines. In other embodiments, the framework may have three, four, five, or six struts, and an equal number of lines arranged around the elongate instrument.
In another embodiment, the struts are mounted on a distal end of a cannula. Each strut may comprise a tubular member having a lumen and each flexible line is carried by the lumen of each tubular strut. The second end of each strut may curve toward the immediately adjacent strut.
In another embodiment, the expansion framework may be equipped with a filter mesh having two edges. A first edge of the mesh attaches circumferentially and continuously about the elongate instrument and is aligned with the first end of each strut. A second edge of the mesh may attach circumferentially to the second end of each strut and/or to a segment of each line which extends beyond the second end of each strut. The elongate instrument may comprise a blood filtration cannula. When the filter mesh is deployed inside a patient""s blood vessel, as the second end of each strut expands radially outward, and the filter mesh also expands radially outward to contact the vessel wall. After embolic materials are collected from the blood onto the filter mesh, the mesh and struts are collapsed, and the cannula is removed.
In an alternative embodiment, the elongate instrument comprises a percutaneous catheter. The catheter may include a balloon occluder. The balloon occluder may be mounted proximal the struts. This embodiment provides occlusion of the blood vessel, such as aortic occlusion in open heart procedures (e.g., valve repair), in addition to providing an expansion mechanism for a filter or other medical devices. Using this construction the filter is disposed between the occluder and the heart and captures debris (which accumulates in the heart and aortic root during bypass) when the heart resumes beating and the occluder is removed. For an extensive discussion of the use of percutaneous filtration catheters of this type for prevention of stoke following valve repair surgery, the reader is referred to Jang, U.S. application Ser. No. 09/170,359, filed Oct. 13, 1998, which is incorporated herein by reference.
The methods of the present invention include deployment and expanding a portion of a medical device within a patient by using the expansion mechanism as described above. A medical device is inserted into the patient through an incision. The flexible lines are pushed distally by an operator to pay out a portion of each line beyond the end of each strut, to thereby expand the strutted portion of the device radially outward. By manipulating the lines, the operator is able to feel for the contour of an interior vessel wall, thereby minimizing the gap between the medical device and the vessel wall. To remove the medical device, the flexible lines are pulled proximally to contract the strutted portion of the device radially inward, and the device is removed from the patient.
In a preferred method, a cannula is equipped with a filter mesh disposed over the struts, and the filter mesh is expanded by pushing the flexible lines distally. During cardiac surgeries, such as valve repair surgery, the filter mesh captures embolic materials which are released from the heart or aorta. During carotid endarterectomy, the filter mesh entraps calcium and atheromatous debris from the carotid artery. After a surgical procedure is accomplished, the flexible lines are pulled and the filter mesh is contracted tightly against the elongate element. In this method, the trapped emboli are secured by the tight compliant framework during removal.
It will be understood that there are several advantages in using the framework described above. For example, (1) the filter frame and chassis allow for perfusion of fluid or blood through the center of the expansion mechanism; (2) trapped emboli are secured within a filter mesh when the wire frame is drawn closed and tight; (3) the expansion mechanism provides an operator feedback of contact between the devices and vascular wall; (4) a filter expansion mechanism may be combined with a balloon occluder and/or xe2x80x9cdirect stickxe2x80x9d access device; and (5) the framework can adjust to a wide range of blood vessel diameter.